There is a conventional light emitting device as shown in FIGS. 6A and 6B (see JP 2011-34674 A (PTL 1)).
The light emitting device 100 shown in FIGS. 6A and 6B has a lead frame 101, a light emitting element 102 on the lead frame 101, a sealing resin 103 on the lead frame 101 for sealing the light emitting element 102, and a case member 104 made of resin for covering the sides of the sealing resin 103. The lead frame 101 and the light emitting element 102 are connected to each other by wires 105. An upper end surface 103a of the sealing resin 103 defines an aperture through which light emitted from the light emitting element 102 goes out.
The light emitting device 100 has been used as a backlight device, as shown in FIG. 7. As shown in FIG. 7, a plurality of light emitting devices 100 are arranged in a line and a light guide body 106 is disposed opposite to the upper end surfaces 103a of the sealing resins 103 of the light emitting devices 100.
The light guide body 106 is plate-shaped and has an end surface 106a opposed to the upper end surfaces 103a of the sealing resins 103 of the light emitting devices 100. Light emitted through the upper end surfaces 103a of the sealing resins 103 is taken into the light guide body 106 through the end face 106a of the light guide body 106. Then, the light is diffused and reflected within the light guide body 106 and taken out through a planar surface 106b of the light guide body 106. The light taken out through the planar surface 106b is used as backlight for liquid crystal panels and advertisement films.
As shown in FIG. 8, the backlight device is designed such that there is a space or interval of about 1 mm between the light emitting devices 100 and the light guide body 106 in order to prevent the light guide body 106 from directly touching the light emitting devices 100.
FIG. 9A shows a sectional view of the backlight device taken perpendicularly to a thickness direction of the light guide body 106. FIG. 9A shows a normal positional relationship between the light emitting device 100 and the light guide body 106 in which there is a sufficient spacing or interval therebetween to avoid a possible collision of the light emitting device 100 and the light guide body 106. In the state shown in FIG. 9A, a portion of a light beam emitted from the light emitting element 102 of the light emitting device 100 does not enter the light guide body 106, as indicated by dotted arrow A.
FIG. 9B shows a state that the light guide body 106 is positioned closer to the light emitting device 100 than when the light guide body 106 and the light emitting device 100 assume their positions shown in FIG. 9A. In the state shown in FIG. 9B, the portion of the light beam that does not enter the light guide body 106 in the state shown FIG. 9A is now allowed to enter the light guide body 106 as indicated by dotted arrow A.
As is apparent from above, a shorter distance between the light emitting device 100 and the light guide 106 enables light from the light emitting device 100 to enter the light guide body 106 with increased efficiency.
If, however, the light emitting device 100 is approached to the light guide body 106 to the extent that the light emitting device 100 nearly touches the light guide body 106 as shown in FIG. 10A, when the light emitting device 100 turns on or a surrounding temperature rises, there is a risk of collision of the light guide body 106 against the light emitting device 100 due to thermal expansion of the light guide body 106 as shown by an arrow in FIG. 10B.
When the end surface 106a of the light guide body 106 collides against the case member 104 of the light emitting device 100, there raises a problem that the case member 104 may have cracks C as shown in FIG. 11 if the case member 104 does not have enough strength. Also, the cracks may cause breaking or disconnection of the wires 105 (shown in FIG. 6B) within the sealing resin 103.
The above problems can happen for real. Thus, regarding planned dimensions, a very important selection must be made between increase of an amount of light incident upon the light guide body 106 and reduction of probability of the risk of wire breaking or disconnection due to the thermal expansion of the light guide body 106.